[CORD-46] Create a broadcast group for each subnet

DONE
- Expose subnet-to-ports information from DeviceProperties and DeviceConfiguration
- Create subnetNextObjectiveStore to store <DeviceId, IpPrefix> to nextId mapping
- Implement broadcast NextObjective in SpringOpenTTP
      Use ALL group type to achieve broadcast

TODO (not in this submission)
- Push ARP table for a host when its location is learned
- Push default ARP table miss rule. Action = to the broadcast group

Change-Id: I2de28095e85289e75af3fc7a02c811b270b342ad
diff --git a/src/main/java/org/onosproject/segmentrouting/grouphandler/SubnetNextObjectiveStoreKey.java b/src/main/java/org/onosproject/segmentrouting/grouphandler/SubnetNextObjectiveStoreKey.java
new file mode 100644
index 0000000..d6b16c7
--- /dev/null
+++ b/src/main/java/org/onosproject/segmentrouting/grouphandler/SubnetNextObjectiveStoreKey.java
@@ -0,0 +1,78 @@
+/*
+ * Copyright 2014-2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.segmentrouting.grouphandler;
+
+import org.onlab.packet.IpPrefix;
+import org.onosproject.net.DeviceId;
+
+import java.util.Objects;
+
+/**
+ * Class definition of Key for Subnet to NextObjective store.
+ */
+public class SubnetNextObjectiveStoreKey {
+    private final DeviceId deviceId;
+    private final IpPrefix prefix;
+
+    public SubnetNextObjectiveStoreKey(DeviceId deviceId,
+                                       IpPrefix prefix) {
+        this.deviceId = deviceId;
+        this.prefix = prefix;
+    }
+
+    /**
+     * Gets device id in this SubnetNextObjectiveStoreKey.
+     *
+     * @return device id
+     */
+    public DeviceId deviceId() {
+        return this.deviceId;
+    }
+
+    /**
+     * Gets subnet information in this SubnetNextObjectiveStoreKey.
+     *
+     * @return subnet information
+     */
+    public IpPrefix prefix() {
+        return this.prefix;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (!(o instanceof SubnetNextObjectiveStoreKey)) {
+            return false;
+        }
+        SubnetNextObjectiveStoreKey that =
+                (SubnetNextObjectiveStoreKey) o;
+        return (Objects.equals(this.deviceId, that.deviceId) &&
+                Objects.equals(this.prefix, that.prefix));
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(deviceId, prefix);
+    }
+
+    @Override
+    public String toString() {
+        return "Device: " + deviceId + " Subnet: " + prefix;
+    }
+}